1. Field of the Invention
The present invention relates to a stepping motor controller and an analog electronic timepiece using the stepping motor controller.
2. Description of the Related Art
Conventionally, a stepping motor is used in an analog electronic timepiece and the like. The stepping motor includes: a stator having a rotor-containing hole and a positioner for determining a rotor stopping position; a rotor disposed in the rotor-containing hole; and a coil. Also, the stepping motor is adapted to rotate the rotor by applying alternating signal to the coil to generate magnetic flux in the stator, and to stop the rotor at a position corresponding to the positioner.
In conventional electronic timepieces including a stepping motor controller for driving a stepping motor with a minimum energy, the stepping motor is driven by a plurality of drive pulses, as inventions described in JP-B-63-018148, JP-B-63-018149, and JP-B-57-018440. When the stepping motor controller receives a detection result from a rotation detector and determines that the stepping motor is not rotating, the stepping motor controller pulses up (ranks up) a main drive pulse to that having larger energy, and repeats this until the stepping motor can be driven by the main drive pulse. Also, the stepping motor controller pulses down (ranks down) the main drive pulse to that having smaller energy at regular time intervals to determine whether the main drive pulse is excessively pulsed up or not. The stepping motor controller can determine the margin for driving the stepping motor based on when an induced voltage (detection signal) exceeding a predetermined reference threshold voltage has been detected, and if determines that there is no margin for driving, does not pulse down the main drive pulse. Thus the stepping motor controller can control the rotation of the stepping motor while reducing power consumption.
However, when initializing the driving (such as powering on or resetting), the main drive pulse having small energy may stop the motor.
In order not to stop the motor, starting with the main drive pulse with a sufficient margin for driving may cause the motor to rotate. In this case, however, large consumption current flows until the main drive pulse is pulsed down to that for normal driving, which raises a problem of wasting energy for a long time.
Also, in this period, consumption current is measured to be higher than that in normal driving. So, in order to measure correct consumption current, the measurement should be performed after the main drive pulse is pulsed down to an optimum one through the repetition of pulsing down at regular time intervals.